Messages in this thread | | | Date | Fri, 29 Aug 2008 00:21:27 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH RFC] x86: check for and defend against BIOS memory corruption |
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Ingo Molnar wrote: > * Rafał Miłecki <zajec5@gmail.com> wrote: > > >> 2008/8/28 Jeremy Fitzhardinge <jeremy@goop.org>: >> >>> Some BIOSes have been observed to corrupt memory in the low 64k. This >>> patch does two things: >>> - Reserves all memory which does not have to be in that area, to >>> prevent it from being used as general memory by the kernel. Things >>> like the SMP trampoline are still in the memory, however. >>> - Clears the reserved memory so we can observe changes to it. >>> - Adds a function check_for_bios_corruption() which checks and reports on >>> memory becoming unexpectedly non-zero. Currently it's called in the >>> x86 fault handler, and the powermanagement debug output. >>> >>> RFC: What other places should we check for corruption in? >>> >>> [ Alan, Rafał: could you check you see: >>> 1: corruption messages >>> 2: no crashes >>> Thanks -J >>> ] >>> >> I was trying my best to crash system with this patch applied and failed :) >> >> Works great. >> >> Just wonder if I should expect any printk from >> check_for_bios_corruption? I do not see any: >> >> zajec@sony:~> dmesg | grep -i corr >> scanning 2 areas for BIOS corruption >> > > that's _very_ weird. >
No, it's expected. Rafał only got corruption when plugging his HDMI cable, and I didn't put any corruption checks on that path (I'm not even sure what kernel code would get executed in that case). Hugh's original patch put a check in the hot path of the fault handler - and so it would get called regularly - but I put it in the kernel-bug path, which is fairly pointless given that we expect this patch to prevent the crashes.
It does, however, do the check in the pm state changes, so doing a suspend should make it print some of the corruption it found. Alan's case would be a better test for that though.
It does raise the question of where the good places to put the check are. It shouldn't be too hot, given that it's scanning ~64k of memory, but often enough to actually show something. I was thinking of putting some calls in the acpi code itself, but got, erm, discouraged.
Maybe hooking into a sysrq key would be useful (sysrq-m?).
> maybe the BIOS expects _zeroes_ somewhere? Do you suddenly see crashes > if you change this line in Jeremy's patch: > > + memset(__va(addr), 0, size); > > to something like: > > + memset(__va(addr), 0x55, size); > > If this does not tickle any messages either, then maybe the problem is > in the identity of the entities we allocate in the first 64K. Is there a > list of allocations that go there when Jeremy's patch is not applied? > > but ... i think with an earlier patch you saw corruption, right? > Far-fetched idea: maybe it's some CPU erratum during suspend/resume that > corrupts pagetables if the pagetables are allocated in the first 64K of > RAM? In that case we should use a bootmem allocation for pagetables that > give a minimum address of 64K. >
Rafał's corruption was definitely non-zero. I think the corruption is happening, but it's just not reported.
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